Page 248 - Veterinary Immunology, 10th Edition

• Explain how the adaptive immune system is optimized to recognize microbial
VetBooks.ir • Understand why the best antigens are therefore large, complex, stable, foreign
macromolecules, especially, but not exclusively, proteins.

proteins.
• Explain why small molecules of less than 5 kDa are usually poor antigens.
• List important bacterial and viral antigens.

• Describe how small molecules may be made antigenic by linking them to large
proteins to act as haptens.
• Recognize that the cells of the adaptive immune system use receptors that can

recognize specific sites on the surface of foreign molecules.
• Define antigenic determinant, epitope, hapten, antigenicity, autoantigen, and
cross-reaction.

• List the key factors that influence antigenicity.

Up to now we have considered only the body's innate reactions to
microbial invasion. Innate responses are triggered by recognition of
a limited number of conserved microbial pathogen-associated

molecular patterns (PAMPs) such as microbial nucleic acids or
lipopolysaccharides. The triggering of inflammation and the
mobilization of phagocytic cells such as neutrophils and

macrophages by these molecules contributes to the rapid
destruction of microbial invaders. Although effective in the short
term, innate immunity cannot be guaranteed to provide complete
resistance to infection. Nor does the body learn from the experience.
Thus a more potent immune response should ideally recognize all

the foreign molecules on an invading microbe. In addition, such a
response should be able to learn from this experience and, given
time, evolve more efficient procedures to combat subsequent

invasions. This new and improved response is the function of the
adaptive immune system.
During an adaptive immune response, molecules from invading
organisms are captured, processed, and presented to the cells of the
immune system. These cells have surface receptors that can bind

appropriately presented molecules. These bound molecules or
antigens then trigger a powerful immune response that ensures an
animal's survival. In addition, the immune system “remembers”

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